Growth, development, reproduction and yield of silkworms depend on the availability
and supply of preferred host plants having good agronomic and nutritional characteristics.
Eri-silkworm, Samia cynthia recini B. is a multivoltine and polyphgous
insect feeding on diversified host plants among which castor is a primary host
plant. There is differential preference for the different varieties of castor
by S.c. ricini. In the present study, eight different castor genotypes;
namely Abaro, Acc 106584, Acc 203241, Acc 208624, Ar sel, Bako, GK sel and local
were evaluated for their merits as feed and nutritional sources for white plain
S.c. ricini at Melkassa Agricultural Research Center, Ethiopia. The treatments
were arranged in a Completely Randomized Design (CRD) in three replications.
Fifty worms were used in each replication. Significant difference was observed
in rearing performance of eri-silkworms when fed to leaves of different castor
genotypes. Among castor genotypes fed to eri-silkworm, Abaro fed worms showed
medium to maximum records of matured larval weight (8.17 g), effective rate
of rearing (74.68%), survival rate (76.08%), cocoon weight (3.34 g), pupal weight
(2.86 g), shell weight (0.48 g), silk ratio (14.49%), fecundity (382.00), hatchability
(88.17%) and shorter larval duration (584.17 h). In conclusion, genotype Abaro
was superior to the other genotypes in improving the rearing performance of
eri-silkworms and can be recommended for further research and development work
in integrating silkworm activities for silk and oil seed productions.

Silk is a functional term used to describe natural-protein fibers that are
secreted by arthropods (Chowdhary, 2006). Silk production
has the potential to make a significant contribution to the economy of many
countries where there is surplus labor, low-costs of production and a willingness
to adopt new technologies (Hajare et al., 2007).

Silk has strong affinity to the people of Ethiopia starting from ancient period
of Axum Kingdom. However, the silk yarns used were imported from India, Arabia
and China though the country has diversified climate and vegetation to support
diversified options of silk industry (Spring and Hudson,
2002). Belli (1947) reported that there were no
known records of silk being produced in the country until 1930s. Currently,
Ethiopian is the second populous country in Africa after Nigeria. There is a
general trend of increasing unemployment. Therefore, sericulture, an agro based
labour intensive and environment friendly cottage industry, can become an efficient
and effective agricultural endeavor for the country. The business holds a ray
of hope at village level for Ethiopian citizen migrating to cities searching
jobs. Though, several research and development efforts were attempted on silkworms,
in Ethiopia in the past decade including eri silkworms, none of them resulted
in large scale production of silk like Asian and some African countries. As
a result, silk production from eri silkworm is practiced bits in bits in different
parts of the country especially by poor farmers as an additional income source
through efficient use of family labor (Metaferia et al.,
2007).

Castor grows widely and abundantly in many parts of Ethiopia. In addition to
cultivated castor on cultivable lands, it is also found wild in waste places,
fallow fields, along road sides and irrigation canals among others (Metaferia
et al., 2007). It is dominantly used for oil seed production; however,
it is also used for rearing of eri-silkworms especially in the rift valley areas
and southern region of Ethiopia.

Eri silkworm larvae feed on castor leaves to obtain essential nutrients for
their growth, survival, production of silk cocoon and reproduction. Thus, successful
eri silk production depends on nutritive value of castor leaves. Krishnaswami
et al. (1970) reported that the growth and development of eri-silkworm
larvae, reproductive capacity of adults and the quality of silk produced are
highly dependent on the quality of castor leaves fed to the worms. Growth, development
and economic traits of silkworms are influenced by the host plants and their
nutritive contents (Singh and Das, 2006). However, castor
shows a wide range of diversity in nature. It has been well recognized that
morphological features and nutritive values of the leaves differ significantly
from variety to variety and over locations. Patil et
al. (1998) has reported significant variation in performance of eri-silkworms
when different castor genotypes were fed to the different instars of the larvae.
An extensive study has been made in India on larval growth and rearing performances
of eri-silkworm as influenced by host plants.

Hence, it can be recognized that selection of castor genotypes is an important
criterion for better growth and development of eri-silkworm larvae to obtain
better fecundity, silkworm development and cocoon productivity. However, the
differential performance of eri-silkworm on different castor genotypes has not
been researched and documented in Ethiopia. Therefore, this work was carried
out to know the influence of castor genotypes on rearing performance of eri-silkworms
to identify promising castor genotype for integrated production of silk and
seed oil.

MATERIALS AND METHODS

Description of the study site: The study was conducted at Melkassa Agricultural
Research Center (MARC), which is one of the Research Centers under the Ethiopian
Institute of Agricultural Research (EIAR). It is found 117 km away from Addis
Ababa and 17 km to southeast of Nazareth in the East-Shewa zone of Oromia regional
state in Ethiopia. It is located 8°24'N latitude and 39°12'E longitude
having an elevation of 1550 m above sea level and a mean annual rainfall of
770 mm.

Experimental procedures: White plain eri-silkworm breed was used for
the experiment. It was reared on eight castor genotypes, which were procured
from oilseeds research division of MARC and Institute of Biodiversity Conservation.
The castor genotypes were planted and managed similarly as per the recommended
package of practices for the crop in the area. The experiment was designed in
a Completely Randomized Design (CRD) and the treatments were replicated thrice.
In each replication, 50 worms were used and allowed to complete the larval period
on the selected genotype of castor. The silkworm rearing room and equipments
were cleaned, washed and disinfected with 2% formalin solution at the rate of
800 mL 10 m-2 before the commencement of the experiment (Dayashankar,
1982). This breed was reared following cellular rearing techniques starting
from brushing till cocoon spinning on the eight genotypes. Tender leaves of
castor were fed four times a day until the larvae ends 2nd instar stage and
semi tender leaves to 3rd instar, while more matured leaves were fed to 4th
and 5th instar larvae.

Matured worms were picked and mounted on the mountages for spinning. On the
sixth day of spinning, the cocoons were harvested, counted and weighed (Singh
and Benchamin, 2002).

The result of the experiment, i.e., rearing performances of eri-silkworms in
relation with egg, larval and cocoon traits as influenced by different castor
genotypes were presented hereunder.

Fecundity: Silkworm fed on Acc 106584 showed significantly higher fecundity
(409 eggs/female) followed by GK sel (389 eggs/female) and Abaro (382 eggs/female).
The local check, which was at par with Ar sel and Acc 203241, was lower performing
compared to the rest of the castor genotypes for fecundity (Fig.
1).

Hatchability: Similarly, hatching percentage showed significant variation
when larvae of eri-silkworm were fed on different castor genotypes. Hatching
percentage ranged from minimum of 81.50% for Acc 203241 to maximum of 95.33%
for Acc 106584. The next best genotype in improving the hatching percentage
of moths was genotype GK sel (93.83%) followed by Abaro (88.17%). The local
genotype showed better hatching percentage than Acc 203241 and Ar sel only (Table
1).

Larval duration: Eri-silkworm larval duration has also showed significant
variation when silkworms were supplied with different castor genotypes. Significantly
longer larval durations (604.17 h) were recorded from the worms fed on Bako.
However, there was no significant difference among other castor genotypes which
showed a range of 588.17-592.17 h larval duration.

Survival rate: The survival rate of silkworm larvae on different castor
genotypes showed significant variation. The highest survival rate was recorded
from silkworms reared on Acc 208624 (78.349%) followed by GK sel (77.748%),
Bako (77.656%), Acc 108584 (76.494%) and Abaro (76.079%). The least survival
rate was recorded from the local check (66.117%) (Table 1).

*Means followed by the same letter within a column are not
significantly different from each other at 5% level of significance

Fig. 1:

Effect of castor genotypes on fecundity of eri-silkworm moths

ERR (%): Effective Rate of Rearing (ERR), which reveals percentage of
the number of cocoons harvested to number of larvae brushed, has also showed
a significant difference when eri silkworms were fed on different castor genotypes.
Eri silkworm fed on Abaro registered maximum ERR (74.68%) closely followed by
Acc 203241 (73.38%), Acc 208624 (73.18%) and Bako (73.15%). The least ERR was
obtained from local check (65.36%) (Table 1).

Matured larval weight: Weight of a single matured silkworm larva was
significantly different among the treatments. Matured worms fed on Bako and
Abaro recorded significantly higher larval weight, 8.20 and 8.17 g, respectively.
However, the least larval weight was obtained from worms fed on local check
(7.60 g) (Fig. 2).

Cocoon traits: With respect to cocoon traits, maximum and significantly
different single cocoon weight was recorded from those larvae which were fed
with the leaves of Abaro (3.344 g) followed by Acc 208624 (3.307 g). Minimum
single cocoon weight (3.131 g) was recorded from larvae fed on Acc 203241 but
this genotype was statistically on par with local (3.144 g) and Acc 106584 (3.149
g) genotypes in single cocoon weight performance. Similarly, the highest and
significant single pupa weight was obtained from worms fed on Abaro (2.860 g)
and the lowest was obtained from those fed on Acc 203241 (2.684 g) (Table
2).

Effects of castor genotypes on cocoon, pupal and shell weight
and cocoon shell ratio of eri-silkworms

*Means followed by the same letter within a column are not
significantly different from each other at 5% level of significance

Fig. 2:

Effect of castor genotypes on eri-silkworms single larval
weight (g)

Similar to single cocoon shell weight, silk ratio was found to be significantly
higher in Abaro (14.487%) closely followed by Bako (14.471%) and Acc 203241
(14.458%), while the lowest was recorded from the local check (14.07%) (Table
2).

DISCUSSION

Rearing performance study on eri-silkworm as influenced by castor genotypes
was carried out and differences in these genotypes were evaluated based on different
response variables measured from the worms fed with the leaves of the genotypes.
In general, the results indicated that castor genotypes viz., Abaro, Acc 106584,
Acc 203241, Acc 208624, Ar sel, Bako, GK sel and local check resulted in significant
variation in rearing performances of the worms. It is a well documented fact
that insects do vary in efficiency of conversion of digested food due to the
varied level of nutrients intake, quality of the food and total biochemical
components of the leaf supplied to the insects (Sengupta
et al., 2008).

In general, among castor genotypes studied, silkworms fed on Abaro gave the
highest cocoon weight, shell weight, pupal weight, silk ratio and ERR. With
respect to hatching percentage, larval weight, fecundity and survival rate;
the same genotype was the second or the third best. On the other hand, Acc 208624
fed worms showed the highest survival rate with above medium records for the
rest of the variables measured. The difference in the rearing performances of
eri-silkworms could be attributed to the differences in the nutritional composition;
such as moisture, proteins, carbohydrates, minerals, fat, vitamins, etc., of
the leaves of the different castor genotypes. Similar studies conducted by Patil
et al. (2009), Jayaramaiah and Sannappa (1998)
and Sengupta et al. (2008) in India found differences
in larval, cocoon and post cocoon traits of eri-silkworms when fed with different
castor genotypes. Besides, Sannappa et al. (2007)
mentioned variation in larval, cocoon and grainage variables for eri-silkworms
when fed on different castor genotypes in South India. They recommended Aruna
castor variety for rearing of eri-worms for commercial traits. Eri silkworms
silk production depends on the amount of feed provided to the larvae, the rate
at which the feed is provided and quantity of leaf consumed by the larvae. These
in turn influence the growth rate, development time, body weight, survival percentage,
intensity of silk secretion, adult emergence, mating success and extent of reproduction
(Sannappa et al., 2007).

In this particular study, genotype Bako fed worms resulted in the highest larval
weight, but with longer larval duration and lower weights of cocoons, pupae
and cocoon shell. Similar findings by Jayaramaiah and Sannappa
(1998) confirmed castor genotypic differences on feeding efficiency of eri
silkworms. Food consumption rate of eri-silkworm may depend on the phagostimulant
nature of the leaf, existing physical factors, nature of leaf and moisture content
of leaf of castor genotypes. El-Shaarawy et al.
(1975) opined that bloomy red variety of castor is preferred from bloomy
green variety by eri silkworm larvae. Many researchers on eri-silkworm vis-à-vis
host plant relationship such as Sannappa et al.
(2002) and Govindan et al. (2005) registered
variations in total food consumption among different castor genotypes when offered
as food to eri silkworm both on fresh and dry weight basis.

Furthermore, local genotype fed silkworms recorded minimum values for
most rearing performance indicators. It may be because its leaf contains less
of important nutrients and/or has lower efficiency to be converted to larval,
cocoon and post cocoon traits of eri silkworms. Or it may be due to the presence
of some anti-nutritional components like high amount of fiber or some protein
binding tannins in the leaf of local variety. Therefore, the present study revealed
that Abaro, which showed 3.344 and 0.484 g single cocoon weight and single shell
weight, respectively, is the most promising castor genotype with respect to
cocoon traits and other rearing variables. It is comparable with findings of
Patil et al. (1998) who obtained single cocoon
and shell weights of 3.817 and 0.4433 g, respectively in a selected castor genotype
called RG-323 in India. Moreover, Abaro genotype was even better performing
than 2.132 and 0.339 g of single cocoon and shell weights, respectively, obtained
from the selected Aruna genotype by Sannappa and Jayaramaiah
(1999).

CONCLUSION AND RECOMMENDATIONS

The present study revealed that castor genotypes have strong influence on eri
silkworm rearing performance. Hence, selection of castor genotypes for rearing
eri silkworm based up on rearing performance of eri silkworms is very important
in order to get better egg production, larval development and cocoon yield.
Therefore, castor genotype named Abaro was found to be the best promising with
respect to rearing performance indicators of eri silkworm especially with regard
to cocoon traits. Therefore, Abaro genotype of castor is recommended for eri
silkworm research and development efforts in the future in Ethiopia.

However, more research should be carried out to support the current findings
with regard to different pests and disease management options, agronomic practices
and foliar composition studies. Leaf defoliation studies will also be required
to be studied to integrate eri silkworm rearing with castor oil seed production
in the future.

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Metaferia, H.Y., T. Amanuel and S. Kedir, 2007. Scaling up of silk production technologies for employment and income generation in Ethiopia. Proceedings of the International Conference on Scaling Up and Scaling Out of Agricultural Technologies in Ethiopia, May 9-11, 2006, Ethiopian Institute of Agricultural Research, Addis Ababa, Ethiopia -.

Sakthivel, N., 2004. Eri culture on castor and tapioca in Tamil Nadu. Proceeding of the Workshop of Prospects and Development of Ericulture, University of Agricultural Sciences, (WPDE'04), Dharwad, pp: 78-81.

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